They are somewhat effective, if you have ever lived next to a highway you would be able to tell.

Obviously, they won't make those massive farms 100% silent, from personal experience, I was able to hear "very slightly" the noise from my farm from a 2 km distance, it was on a quiet winter night, obviously, if you don't know where the sound is coming from, at that distance it would just sound like a truck engine somewhere a bit far, but once your ears grasp what miners noise actually is, you will be able to tell, the whistling sound that miners make due to heatsink design and high RPMs is exceptional.

Many people underestimate the noise level that miners make, but in a farm where we had no more than 200 something miners, right on the exhaust side, it was as loud as 120-130db, which is as loud as a jet, powerful it could break your ear drum if you stay there for too long without wearing ears protection.

One thing that would bring the noise level down close to silent for those who live like 1000 meters away would be to get the fans to spin below 3000RPM, that's when they get very quiet, if they spin anywhere near 7000RPM no sound barrier on planet earth would stop the noise from traveling a few kilometers away.